It will depend on your local building and housing codes.

The current owner is a family friend that’s been in the business for 30+ years but is very old school and still runs the business off a system he coded in DOS back in the 90’s.

However, as your first capitalization and not doing it as a matter of practice in my layman's opinion isn't building a case of using the LLC as an alter-ego. 

There are countless contractors out there offering "cash discounts", which is secret code for I don't pay taxes.

The only requirement in the code and regulations is that you have the intent to hold the properties for rental, investment or business use (as opposed to flipping or holding for sale). 

The 75056 zip code is shared between the newer part of The Colony and Castle Hills in Lewisville.

With the current code trying to build a triplex in that same spot can be challenging, not to mention the current cost of lumber.

Your path on what will work best does depend on the Local Code. 

A nonconforming use is a use of land, buildings, or structures that was lawfully established prior to the effective date of this ordinance, or any amendment thereto, but which does not conform to the regulations for the zoning classification in which it is located.Nonconforming uses may be continued subject to the following limitations:a) No nonconforming use shall be extended, expanded, enlarged, or moved to occupy a different or greater area of land, buildings or structures than was occupied by such use at the time it became nonconforming; provided, however, a nonconforming use may be extended throughout any parts of a building which were specifically designed and arranged for such use at the time it became nonconforming.b) No building or structure devoted to a nonconforming use shall be enlarged, extended, recon­structed, moved, or structurally altered unless such building or structure is thereafter devoted to a conforming use; provided, however, such building or structure may be enlarged or extended upon prior authorization from the Board of Adjustment, which authorization shall not be granted unless the Board of Adjustment makes each of the following findings of fact:1) The proposed enlargement or extension shall be de minimis in relation to the existing building or structure.2) The proposed enlargement or extension shall not increase the intensity of the nonconforming use, which is to say, it will not result in an increase in dwelling units for a residential use nor in gross floor area for a nonresidential use.3) The proposed enlargement or extension is designed so that it will not render the use of the property any less compatible than it is in its existing circumstances.4) The authorization of such proposed enlargement or extension is not otherwise contrary to the public health, safety or welfare.c) A nonconforming use of a structure may not be changed to another nonconforming use unless such change is authorized by the Board of Adjustment.

My question is for the underground pipe, is it required by code to use Schedule 80 PVC in Massachusetts?